Gas and liquid piping systems utilizing corrugated stainless steel tubing (“CSST”) and fittings can be designed for use in combination with elevated pressures of up to about 25 psi or more and provide advantages over traditional rigid black iron piping systems in terms of ease and speed of installation, elimination of onsite measuring, and reduction in the need for certain fittings such as elbows, tees, and couplings. Undesirably, the thin metal walls are vulnerable to failure when exposed to physical or electrical forces, such as lightning or fault currents.
Often, electrical currents will occur inside a structure. These electrical currents can be the result of power fault currents or induced currents resulting from lightning interactions with a house or structure. The term “fault current” is typically used to describe an overload in an electrical system, but is used broadly herein to include any electrical current that is not normal in a specific system. Electrical currents from lightning can reach a structure directly or indirectly. While both direct and indirect currents may enter a structure through a particular system, voltage can be induced in other systems in the structure, especially those in close proximity to piping systems. This can often result in an electrical flashover or are between the adjacent systems. A flashover occurs when a large voltage differential exists between two electrical conductors, causing the air to ionize, the material between the conductive bodies to be punctured by the high voltage, and formation of a spark.
It usually takes a very large voltage differential to create a flashover through a good dielectric material. When a flashover does occur, the flow of electrons through the ionized path causes energy dissipation through heating and a shockwave (i.e., sound). The extent of heat and shock is directly related to the duration and magnitude of the electrical energy in the flashover. Frequently, the voltage required to breakdown a dielectric material is enough to drive a relatively large amount of energy across the associated spark often resulting in damage to both conductors and any material between them. The primary mode of failure is extreme heating and melting of these materials.
Metals are electrically conductive materials, making CSST a very good pathway for electrical currents. This leads to the potential for a flashover if the CSST is installed in close proximity to another conductor within a structure and either one becomes energized. A flashover like this is often the result of a lightning event but it is foreseeable that other events may also be capable a producing a sufficient voltage differential between conductors. It is possible that a flash like this can cause enough heat generation to melt a hole in the CSST, allowing fuel gas to escape. This scenario is worsened by the dielectric jacket that often surrounds CSST. This jacket typically breaks down in a very small area, creating a pinhole as a result of the flashover. This phenomenon focuses the flash and concentrates the heating of the stainless steel inside. The result is a reduced capability of the CSST to resist puncture from flashover compared to un-jacketed pipe.